1. Field of the Invention:
This invention relates to sewing machines in general and more particularly to lock stitch sewing machines in which it is desirable to incorporate the capability of selectively producing blind stitches.
2. Description of the Prior Art:
The formation of blind stitches is particularly useful for home sewing applications when it is desired to secure a hem fold in place in such fashion that the noticeability of the stitches on the face of the garment is minimized. Commercial sewing machines incorporating the capability of producing blind stitches have long been known in the prior art. These machines are not practical for household use however, since they are specialized to produce but one type of stitch. The U.S. Pat. No. 3,986,469 to Ketterer, which issued on Oct. 19, 1976, the teachings of which are incorporated herein by reference, discloses a method for producing a blind stitch which is suitable for use with a household sewing machine. A thread manipulating mechanism for carrying out the teachings of the Ketterer U.S. Pat. No. 3,986,469, which is suitable for use on a household lock stitch sewing machine, is disclosed in U.S. Pat. No. 3,908,569 which also issued to Ketterer on Sept. 30, 1975, the teachings of which are also incorporated herein by reference.
While the mechanism disclosed in the U.S. Pat. No. 3,908,569 to Ketterer Pat. is capable of producing blind stitches, the mechanism incorporated therein for precluding the skipping of stitches is driven by the horizontal motion of the feed dog toward and away from the needle accommodating slot and is dependent on the horizontal feed dog motion which may be adjusted by the sewing machine operator by manipulation of the stitch length regulator. Accurate production of blind stitches using the Ketterer U.S. Pat. No. 3,908,569 mechanism required that the thread deflecting member engage the loop of thread seized by the beak of the loop taker and sweep it in an appreciable arc around the body of the hook needle to produce a certainty that the hook needle would engage the loop of thread. Certain ranges of small feed dog motion which may be acceptable for movement of fabric by the feed dog have been found to produce excursions of the blind stitch thread manipulating mechanism which were inadequate to carry the thread into a reliable position for seizure by the hook needle, with the attendant possibility of producing imperfect stitches. Since the production of a blind stitch involves drawing a loop of thread through a previously formed loop in much the same manner as the production of a chain stitch, the production of an imperfect blind stitch will cause the stitch to unravel.